On 24/07/2017 17:35, Dr. David Alan Gilbert wrote: > * Jay Zhou (jianjay.z...@huawei.com) wrote: >> Hi Dave, >> >> On 2017/7/21 17:49, Dr. David Alan Gilbert wrote: >>> * Jay Zhou (jianjay.z...@huawei.com) wrote: >>>> Qemu_savevm_state_cleanup() takes about 300ms in my ram migration tests >>>> with a 8U24G vm(20G is really occupied), the main cost comes from >>>> KVM_SET_USER_MEMORY_REGION ioctl when mem.memory_size = 0 in >>>> kvm_set_user_memory_region(). In kmod, the main cost is >>>> kvm_zap_obsolete_pages(), which traverses the active_mmu_pages list to >>>> zap the unsync sptes. >>> >>> Hi Jay, >>> Is this actually increasing the real downtime when the guest isn't >>> running, or is it just the reported time? I see that the s->downtime >>> value is calculated right after where we currently call >>> qemu_savevm_state_cleanup. >> >> It actually increased the real downtime, I used the "ping" command to >> test. Reason is that the source side libvirt sends qmp to qemu to query >> the status of migration, which needs the BQL. qemu_savevm_state_cleanup >> is done with BQL, qemu can not handle the qmp if qemu_savevm_state_cleanup >> has not finished. And the source side libvirt delays about 300ms to notify >> the destination side libvirt to send the "cont" command to start the vm. >> >> I think the value of s->downtime is not accurate enough, maybe we could >> move the calculation of end_time after qemu_savevm_state_cleanup has done. > > I'm copying in Paolo, Radim and Andrea- is there anyway we can make the > teardown of KVMs dirty tracking not take so long? 300ms is a silly long time > on only a small VM.
Xiao Guangrong is working on something vaguely related (but different and simpler because it's entirely contained within KVM), which is to make log_sync faster. The Intel folks working on clear containers also would like MemoryListeners to have a better complexity, but that's again separate from the "zapping" of SPTEs. > Can you tell me which version of libvirt you're using? > I thought the newer ones were supposed to use events so they did't > have to poll qemu. > > If we move qemu_savevm_state_cleanup is it still safe? Are there > some things we're supposed to do at that point which are wrong if > we don't. > > I wonder about something like; take a mutex in > memory_global_dirty_log_start, release it in > memory_global_dirty_log_stop. Then make ram_save_cleanup start > a new thread that does the call to memory_global_dirty_log_stop. I don't like having such a long-lived mutex (it seems like a recipe for deadlocks with the BQL), plus memory_region_transaction_commit (the expensive part of memory_global_dirty_log_stop) needs to be under the BQL itself because it calls MemoryListeners. Maybe memory_global_dirty_log_stop can delay itself to the next vm_start if it's called while runstate_running() returns false (which should be always the case)? It could even be entirely enclosed within memory.c if you do it with a VMChangeStateHandler. Thanks, Paolo > Dave > >> Thanks, >> Jay >> >>> However, we would need to be a bit careful of anything that needs >>> cleaning up before the source restarts on failure; I'm not sure of >>> the semantics of all the current things wired into save_cleanup. >>> >>> Dave >>> >>> >>>> Signed-off-by: Jay Zhou <jianjay.z...@huawei.com> >>>> --- >>>> migration/migration.c | 16 +++++++++------- >>>> qmp.c | 10 ++++++++++ >>>> 2 files changed, 19 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/migration/migration.c b/migration/migration.c >>>> index a0db40d..72832be 100644 >>>> --- a/migration/migration.c >>>> +++ b/migration/migration.c >>>> @@ -1877,6 +1877,15 @@ static void *migration_thread(void *opaque) >>>> if (qemu_file_get_error(s->to_dst_file)) { >>>> migrate_set_state(&s->state, current_active_state, >>>> MIGRATION_STATUS_FAILED); >>>> + /* >>>> + * The resource has been allocated by migration will be >>>> reused in >>>> + * COLO process, so don't release them. >>>> + */ >>>> + if (!enable_colo) { >>>> + qemu_mutex_lock_iothread(); >>>> + qemu_savevm_state_cleanup(); >>>> + qemu_mutex_unlock_iothread(); >>>> + } >>>> trace_migration_thread_file_err(); >>>> break; >>>> } >>>> @@ -1916,13 +1925,6 @@ static void *migration_thread(void *opaque) >>>> end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); >>>> >>>> qemu_mutex_lock_iothread(); >>>> - /* >>>> - * The resource has been allocated by migration will be reused in COLO >>>> - * process, so don't release them. >>>> - */ >>>> - if (!enable_colo) { >>>> - qemu_savevm_state_cleanup(); >>>> - } >>>> if (s->state == MIGRATION_STATUS_COMPLETED) { >>>> uint64_t transferred_bytes = qemu_ftell(s->to_dst_file); >>>> s->total_time = end_time - s->total_time; >>>> diff --git a/qmp.c b/qmp.c >>>> index b86201e..0e68eaa 100644 >>>> --- a/qmp.c >>>> +++ b/qmp.c >>>> @@ -37,6 +37,8 @@ >>>> #include "qom/object_interfaces.h" >>>> #include "hw/mem/pc-dimm.h" >>>> #include "hw/acpi/acpi_dev_interface.h" >>>> +#include "migration/migration.h" >>>> +#include "migration/savevm.h" >>>> >>>> NameInfo *qmp_query_name(Error **errp) >>>> { >>>> @@ -200,6 +202,14 @@ void qmp_cont(Error **errp) >>>> if (runstate_check(RUN_STATE_INMIGRATE)) { >>>> autostart = 1; >>>> } else { >>>> + /* >>>> + * Delay the cleanup to reduce the downtime of migration. >>>> + * The resource has been allocated by migration will be reused >>>> + * in COLO process, so don't release them. >>>> + */ >>>> + if (runstate_check(RUN_STATE_POSTMIGRATE) && >>>> !migrate_colo_enabled()) { >>>> + qemu_savevm_state_cleanup(); >>>> + } >>>> vm_start(); >>>> } >>>> } >>>> -- >>>> 1.8.3.1 >>>> >>>> >>> -- >>> Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK >>> >>> . >>> >> > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK >